Valorization of volatile fatty acids-enriched cheese whey by Yarrowia lipolytica for single cell oil production

Food waste and by-products are often valorized through methane production; however, volatile fatty acids (VFAs) from acidogenic digestion can serve as renewable carbon sources for single cell oil (SCO) production. Yarrowia lipolytica, an oleaginous yeast with Qualified Presumption of Safety (QPS) status, can accumulate SCOs up to 20% of cell dry weight (CDW) on sugars and even more on hydrophobic carbon sources. This study, performed within the European project ONE EARTH, investigates SCO production by Y. lipolytica grown on cheese whey, a common dairy by-product, enriched in VFAs via acetogenic fermentation. Ten wild-type strains were screened on minimal medium with 0.2% acetic acid; seven showed good performance. Their growth was monitored for 72 hours across acetic acid concentrations from 0.2% to 1.0%. Strain-specific tolerance was observed. Based on their performance, three strains (Y3, RO3., RO2) were selected and tested on a VFA-enriched medium at 20°C and 5°C for 13 and 20 days, respectively. While growth was slower at 5°C, biomass was higher (Y3: 817.9 mg/100 mL), whereas lipid accumulation increased at 20°C (Y3: 79.8 mg/100 mL, 10% CDW). Fatty acid analysis showed C18:1, C18:2, and C18:3 accounted for 38–46% of total lipids. RO3. had the highest unsaturation index; Y3 yielded the most long- chain unsaturated fatty acids. Y3 was then grown on VFAs, obtained from squacquerone whey, and incubated at 20°C under static and dynamic conditions. Aeration did not enhance fat content (max 13% CDW), while static conditions increased SCO content (mainly composed of C18:1, C18:2, and C18:3, >50%) to 42% after 13 days incubation. These results support Y. lipolytica as a promising biocatalyst to convert dairy waste into valuable lipids for circular economy applications.